Ubiquitin is a small, highly conserved protein composed of 76 amino acids that is post-transcriptionally attached to target proteins, including itself, via a concerted three-step enzymatic reaction. This covalent linkage or isopeptide bond primarily occurs between the C-tenninal glycine of ubiquitin and the ε-amino group of lysine residue(s) on the target protein (Pickart, C. M., Annu. Rev. Biochem., 2001: 503-33). The functional consequence of ubiquitination is determined by the number and linkage topology of ubiquitin molecules conjugated to the target protein. For example, proteins exhibiting Lys48-linked polyubiquitin chains are generally targeted to the proteasome for degradation, while monoubiquitination or polyubiquitin chains linked through other lysines regulate several non-proteolytic functions, including cell cycle regulation (Nakayama, K. I. et al., Nat. rev. Cancer, 6(5): 369-81 (2006)), DNA repair (Bergink, S., et al., Nature 458(7237): 461-7 (2009)), transcription (Conaway, R. C., et al., Science 296(5571): 1254-8 (2002)), and endocytosis (Mukhopadhyay, D., et al., Science 315(5809): 201-5 (2007)). Similar to other posttranslational modifications, ubiquitination is a reversible process counteracted by a family of enzymes known as deubiquitinases (DUBs). These enzymes are cysteine proteases or metalloproteases that hydrolyze the ubiquitin isopeptide bond (Komander, D., et al., Nat. Rev. Mol. Cell Biol. 10(8): 550-63 (2007)). The human genome encodes close to 100 DUBs.
In recent years, the ubiquitin-proteasome system has attracted increasing attention as a novel drug target. DUBs have been recognized as attractive targets for drug discovery since several members of the DUB family have been implicated in processes related to human disease, including cancer and neurodegeneration. Among them, USP1 (ubiquitin-specific protease 1) has gained increased interest as a novel therapeutic target given its roles in DNA damage response. The interaction of USP1 with UAF1 (USP1-associated factor 1), a WD40 repeat-containing protein, leads to the formation of an activated USP1/UAF1 complex, which is required for the deubiquitinase activity. The USP1/UAF1 complex has been found to deubiquitinate monoubiquitinated PCNA (proliferating cell nuclear antigen) and monoubiquitinated FANCD2 (Fanconi anemia group complementation group D2), which are proteins that play important functions in translesion synthesis (TLS) and the Fanconi anemia (FA) pathway, respectively. These two pathways are essential for repair of DNA damage induced by DNA cross-linking agents, such as cisplatin and mitomycin C (MMC). Previous studies have demonstrated that disruption of USP1 or UAF1 in chicken DT40 cells resulted in increased sensitivity to DNA cross-linkers. In addition, knockout of the murine USP1 gene in a mouse model resulted in hypersensitivity to MMC. It also has been demonstrated that inhibiting the cellular activity of human USP1 by pharmacologically active small molecules sensitized non-small cell lung cancer (NSCLC) cells to cisplatin.
The compounds GW7647 and Pimozide have been described as inactivators of USP1. However, both of these compounds are limited by potency and off-target pharmacology, in part because both of these compounds have annotated activity against unrelated targets. Another inhibitor of USP1, C527, which was reported by D'Andrea et al. in WO 2011/137320 A1, sensitizes cells to both the crosslinking agent, mitomycin C, and the topoisomerase I inhibitor, camptothecin. However, C527 shows low micromolar inhibition of related USPs as well as dissimilar DUBs (i.e., UCL-H1 and UCL-H3).
The foregoing shows that there exists an unmet need for new selective inhibitors of the USP1/UAF1 complex, and thus, agents for treating and/or potentiating diseases amenable to treatment or to improvement of treatment, for example, cancer.